This invention relates generally to the equipment for retrieving data from documents which have been recorded on individual frames of a reel of microfilm. More particularly, the present invention relates to an improved interface apparatus for detecting markers on the frames of a reel of microfilm so that a microfilm reader or a microfilm reader printer can be electronically controlled to search for specific documents on a reel of microfilm.
In the initial recording of documents on microfilm, it is common to have each of the page of the document recorded on a separate frame of the film. Hence each frame of the microfilm corresponds to a single page of a document. Typically, the microfilming apparatus places a dark spot called a marker or a "blip" on each frame of the microfilm. Then an index is prepared identifying the document and indicating the microfilm frame on which the document is recorded.
Furthermore, a technique has been employed called batch coding where two distinct tracks on the microfilm are used for blips. A blip is placed in a first track corresponding to each document recorded on the microfilm. A blip is provided in the second track for each group of documents commonly referred to a file or a batch. Since each reel of microfilm may have several thousand frames, it may be appreciated that when it becomes necessary to look at a particular frame of the microfilm, to study a specific document, it is desirable to be able to quickly advance the microfilm through the microfilm reader and to stop the microfilm automatically at the frame on which the particular document has been recorded. The advancing of the microfilm through the reader to locate a particular document is called "scanning" or "searching". Devices already exist for automatically advancing the microfilm through a reader and for sensing and counting the markers or blips in an attempt to scan or search and automatically stop the movement of the microfilm at the desired frame.
However, prior to the present invention, such devices did not permit adjustably positioning the sensors which detect the blips on the microfilm. The sensors were permanently positioned and, therefore, any slight misadjustment resulted in inaccurate counting of blips or markers thus causing the microfilm to be stopped at an incorrect frame.
Furthermore, many microfilm readers and microfilm reader printers do not include the capability of detecting blips. Prior to the present invention, there were no convenient devices which could be retrofit as attachments to the microfilm reader or microfilm reader printer. That is to say, when it was desired to retrofit a microfilm reader or microfilm reader printer prior to the present invention, it was necessary to replace some or all of the microfilm gate area, i.e., the region where the microfilm passes over a light source and is projected onto the screen of the microfilm reader.
The present invention overcomes the shortcomings of the prior art by providing a new and improved universal blip sensor which may be retrofit on already existing microfilm readers and microfilm reader printers and which provides for adjustability of the sensors to provide more accurate detection of microfilm blips.